This kind of filter-manufacturing machine is disclosed in, for example, Japanese Patent Provisional Publication No. Hei 7-203935. This publicly-known manufacturing machine comprises a storage container storing tow formed of filter fibers, and the tow is fed from the storage container along a predetermined feeding path. In the tow feeding process, the tow is opened and spread to be formed into sheet material. Then, plasticizer such as triacetin or the like is added to the sheet material, and the sheet material is supplied toward a rod-forming device. The rod-forming device, while shaping the sheet material into a rod, wraps the rod-shaped sheet material in paper to consecutively form a filter rod.
Since the filter fibers of tow are bonded by plasticizer within the filter rod, the outer shape of the filter rod is stably maintained. Moreover, the hardness of a filter rod is determined by the amount of the added plasticizer, namely, bonding force between the filter fibers. Therefore, in the manufacture of filter rod of this kind, it is necessary to add plasticizer evenly on the whole surface of the sheet material. Conventionally, various methods, such as brush application method, roller transfer method, nozzle spray method, and the like, have been employed for adding the plasticizer. In the case that triacetin is used as plasticizer, the brush application method and the roller transfer method are widely used to add triacetin.
In the case where triacetin is used as plasticizer, triacetin liquefies the surfaces of the filter fibers and then is absorbed thereinto so as to form bond portions between the filter fibers, thus increasing the adhesive strength of the bond portions. Therefore, the filter rod in which triacetin is used as plasticizer, more specifically, the filter plug of a filter cigarette, the filter plug being obtained by cutting the filter rod, keeps low degradation thereof even if left in water.
On the other hand, in the case where a water-soluble material such as polyethylene glycol (PEG) is used as binder in place of triacetin, the filter plug has a high degradation. However, the PEG used as binder is in liquid form only in the state where it is heated as with hot melt adhesive, and the liquid PEG has still higher viscosity than triacetin.
A conventional nozzle used for spraying plasticizer has a low spray pressure, so that the nozzles is capable of spraying only a liquid plasticizer having relatively low viscosity, and incapable of spraying well a liquid material having high viscosity, such as liquid PEG and the like.
On the contrary, if the spray pressure of the nozzle may be increased, the nozzle can spray a certain amount of a liquid material with high viscosity. In this case, however, the liquid material can not be evenly added through the nozzle to the sheet material, making the hardness of the filter rod irregular. Additionally, the liquid material is scattered on machines in the vicinity of the nozzle in the filter-manufacturing machine, which makes it difficult to keep the stable operation of the filter-manufacturing machine.